HPHT vs CVD Lab-Grown Diamonds: Does the Growth Method Matter?
Two ways to grow a diamond: in a press or in a plasma. How HPHT and CVD differ, the clues each leaves inside a stone, and why the individual diamond matters more than the method.
Lab-grown diamonds are made in one of two ways: HPHT (high pressure, high temperature) or CVD (chemical vapour deposition). Buyers often ask which is better. The honest answer is that both produce beautiful diamonds and both produce poor ones, and the grading report of your individual stone matters far more than the method. Still, the differences are interesting, and worth understanding.
HPHT: the pressure cooker
HPHT growth recreates the conditions in which natural diamonds form. A small diamond seed sits in a capsule with a carbon source and a molten metal solvent (typically iron, nickel or cobalt). Huge presses squeeze the capsule at around five to six gigapascals while heating it to roughly 1,300–1,600 °C. Carbon dissolves in the metal and crystallises onto the seed. Modern cubic presses can grow several crystals at once in days to weeks.
Because of the metal solvent, some HPHT diamonds contain tiny metallic inclusions, occasionally enough to make a stone weakly magnetic. Growers add "getters" to keep nitrogen out, which is how colourless HPHT stones are made.
CVD: building diamond from gas
CVD diamonds grow in a vacuum chamber from a mix of hydrogen and methane, energised by microwaves into plasma. Carbon atoms settle on flat diamond seed plates and build up layer by layer over several weeks. CVD diamonds are usually type IIa, a chemically very pure type of diamond. Some come out of the reactor with a brownish tint and are then given a short post-growth HPHT treatment to whiten them.
We cut and polish CVD diamonds ourselves; you can follow the full process in how lab-grown diamonds are made.
What "post-growth treatment" means
Treatment is common, legitimate and permanent, but it should always be disclosed. A grading report from IGI or GIA will note if a lab-grown diamond has been treated after growth, typically in the comments section. A treated diamond is not "worse" by definition; it is simply something you are entitled to know.
So which should you choose?
What actually matters
- Cut quality and proportions
- Colour and clarity grades
- An independent report stating origin and any treatment
- A seller who discloses everything in writing
What matters less
- Whether the stone was HPHT or CVD grown
- Marketing claims that one method is "purer" or "more natural"
The small diamonds in your ring
A halo, a pavé band or an eternity ring can hold dozens of tiny diamonds, called melee. These are rarely graded one by one; they are sorted and checked in parcels for size, colour and clarity. HPHT is widely used to grow small diamonds efficiently, and CVD produces them too. In a lab-grown piece, the accent stones are normally lab-grown as well. In a natural diamond piece, reputable jewellers use screening devices to make sure no undisclosed lab-grown melee has slipped into a parcel.
Three myths about growth methods
- "HPHT is closer to nature, so it is better." Both methods produce real diamond; neither is more "natural" in the finished stone.
- "All CVD diamonds are treated." Many are, to improve colour, but many are sold as grown. The report tells you which.
- "HPHT diamonds always contain metal." Some do; many are perfectly clean to the eye and under magnification.
CVD diamonds cut in our own workshop
Is CVD or HPHT more expensive?
Neither consistently. Price follows the 4Cs, not the growth method.
Can I see whether my diamond is HPHT or CVD?
Not by eye. Check the grading report, which often states the growth method.
Are treated lab-grown diamonds durable?
Yes. HPHT treatment permanently changes the colour and does not weaken the diamond.
Are CVD diamonds always treated after growth?
No. Many are treated to improve colour, but many are sold as grown. Reputable reports state which.
Are the small diamonds in my halo graded?
Usually not individually. Melee is sorted and checked in parcels for size, colour and clarity.
